Infrared luminosity functions of AKARI Sloan Digital Sky galaxies

Goto, Tomostsugu; Arnouts, Stephane; Malkan, Matthew; Takagi, Toshinobu; Inami, Hanae; Pearson, Chris; Wada, Takehiko; Matsuhara, Hideo; Yamauchi, Chrisato; Takeuchi, Tsutomu T.; Nakagawa, Takao; Oyabu, Shinki; Ishihara, Daisuke; Sanders, David B.; Le Floc'h, Emeric; Mok Lee, Hyung; Jeong, Woong-Seob; Serjeant, Stephen and Sedgwick, Chris (2011). Infrared luminosity functions of AKARI Sloan Digital Sky galaxies. Monthly Notices of the Royal Astronomical Society, 414(3) pp. 1903–1913.



By cross-correlating AKARI all sky survey in 6 infrared (IR) bands (9, 18, 65, 90, 140, and 160μm) with the SDSS galaxies, we identified 2357 infrared galaxies with a spectroscopic redshift. This is not just one of the largest samples of local IR galaxies, but AKARI provides crucial FIR bands in accurately measuring galaxy SED across the peak of the dust emission at > 100μm. By fitting modern IR SED models to the AKARI photometry, we measured the total infrared luminosity (LIR) of individual galaxies.

Using this LIR, we constructed the luminosity functions of infrared galaxies at a median redshift of z=0.031. The LF agrees well with that at z=0.0082 (the RBGS), showing smooth and continuous evolution toward higher redshift LFs measured in the AKARI NEP deep field. By integrating the IR LF weighted by LIR, we measured the local cosmic IR luminosity density of IR= (3.8+5.8−1.2) × 108 LMpc−3.

We separate galaxies into AGN (active galactic nuclei), star-forming, and composite by using the [NII]/ vs [OIII]/ line ratios. The fraction of AGN shows a continuous increase with increasing LIR from 25% to 90% at 9< log LIR <12.5. The SFR and L[OIII] show good correlations with LIR for SFG (star-forming galaxies) and AGN, respectively. The self-absorption corrected Hα/Hβ ratio shows a weak increase with LIR with a substantial scatter. When we separate IR LFs into contributions from AGN and star-forming galaxies (SFG), the AGN contribution becomes dominant at LIR > 1011L, coinciding the break of the both SFG and AGN IR LFs. At LIR ≤ 1011L, SFG dominates IR LFs. Only 1.1±0.1% of Ω IR is produced by LIRG (LIR > 1011L), and only 0.03±0.01% is by ULIRG (LIR > 1012L) in the local Universe. Compared with high redshift results from the AKARI NEP deep survey, we observed a strong evolution of ΩSFGIR α(1+z)4.1±0.4 and ΩAGNIR α(1+z)4.1±0.5. Our results show all of our measured quantities (IR LFs, L, ΩAGNIR, ΩSFGIR) show smooth and steady increase from lower redshift (the RBGS) to higher redshift (the AKARI NEP deep survey).

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